A178406 - OEIS

%I #24 Jan 17 2019 13:44:08

%S 2,6,8,12,14,47,88,130,414,1388,1932,4106,4412,12870,22956,23932,

%T 27312,35316,37169,43873,150029

%N Numbers n such that 10^n - 41 is prime.

%C The next term, if one exists, is >100000. - _Robert Price_, Apr 25 2011

%C a(22) > 2.5*10^5. - _Robert Price_, Apr 12 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/aaaba.htm">Near-repdigit numbers of the form AA...AABA</a>.

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/99959.htm#prime">Prime numbers of the form 99...9959</a>.

%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.

%e 10^6 - 41 = 999959 which is a prime number.

%t m=1000; For[n=1, n<m, If[PrimeQ[10^n-41], Print[n]]; n++ ]

%o (PARI) is(n)=ispseudoprime(10^n-41) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A108330, A108328.

%K more,nonn

%O 1,1

%A _Robert Price_, Dec 21 2010

%E a(20)=43873 from _Robert Price_, Apr 25 2011

%E a(21) from Kamada data by _Robert Price_, Apr 12 2015